Solidification method of chromium element in coal gasification ash and obtained low-chromium-mobility large-dosage coal gasification ash-based cemented filling material

Abstract

The invention discloses a method for solidifying chromium in coal gasification ash and an obtained low-chromium-mobility large-dosage coal gasification ash-based cemented filling material, and relates to the technical field of solid waste resource utilization and heavy metal solidification. The curing method comprises the following steps: mixing the coal gasification ash with gangue, steel slag, a cementing material and water to prepare the low-chromium-mobility large-dosage coal gasification ash-based cemented filling material so as to realize the curing of chromium in the coal gasification ash, the cementing material is prepared from the following raw materials: slag and an alkali activator. The low-chromium-mobility large-dosage coal gasification ash-based cemented filling material prepared by the curing method is high in chromium fixing capacity, low in cost, high in coal-based solid waste utilization rate and remarkable in comprehensive benefit.

Description

Technical Field

[0001] The present invention relates to the field of solid waste resource utilization and heavy metal solidification technology, in particular to a method for solidifying chromium elements in coal gasification ash and a low-chromium migration, high-dosage coal gasification ash-based cementitious filling material obtained. Background Art

[0002] Currently, in the field of clean coal utilization, coal gasification technology has been widely promoted due to its efficient and clean utilization of coal resources. However, the chemical composition of the accompanying coal gasification ash is complex and easily induces heavy metal pollution problems. Among them, chromium, especially highly toxic valence states such as hexavalent chromium, has extremely high solubility and mobility. If it leaks into the soil or water, it will spread rapidly, posing a serious threat to the ecosystem and human health. Traditional coal gasification ash treatment methods have poor chromium solidification stability and it is difficult to curb the spread of chromium. Therefore, how to effectively and stably solidify the chromium element in coal gasification ash is the main problem currently faced. Summary of the Invention

[0003] The present invention aims to provide a method for solidifying chromium in coal gasification ash and a resulting high-volume coal gasification ash-based cementitious filling material with low chromium mobility. The present invention uses steel slag and mineral slag as the solidifying materials for chromium in coal gasification ash. By adding an alkaline activator to activate the activity of the coal gasification ash, steel slag, and mineral slag, the chromium in the coal gasification ash is effectively and stably solidified.

[0004] To achieve the above object, the present invention provides the following solutions:

[0005] One of the technical solutions of the present invention is a method for solidifying chromium in coal gasification ash, which comprises mixing coal gasification ash with gangue, steel slag, a cementitious material, and water to prepare a low-chromium migration, high-dosage coal gasification ash-based cementitious filling material to solidify the chromium in the coal gasification ash.

[0006] The raw materials of the cementitious material include slag and an alkali activator.

[0007] The present invention utilizes gangue, steel slag, and a cementitious material to solidify the chromium in coal gasification ash. The alkaline oxides in the steel slag neutralize the acidity of the coal gasification ash, thereby promoting the precipitation of chromium. The gangue possesses certain physical adsorption properties, allowing it to adsorb and fix chromium-containing substances. Simultaneously, under the stimulation of an alkaline activator, the gangue, slag, and the steel slag in the cementitious material form a relatively stable gelled phase, further solidifying the chromium. The synergistic combination of gangue, steel slag, and the cementitious material effectively solidifies the chromium in the coal gasification ash, significantly reducing the mobility of chromium in the resulting high-volume coal gasification ash-based cementitious filling material.

[0008] Furthermore, steel slag, ore slag, and gangue are all large quantities of industrial solid waste, not only occupying land resources but also having a negative impact on the ecological environment. The present invention utilizes steel slag, ore slag, and gangue to solidify the chromium element in coal gasification ash, not only producing a high-performance cementitious filling material but also realizing resource utilization of industrial solid waste.

[0009] Furthermore, the coal gasification ash includes coarse coal gasification ash and fine coal gasification ash.

[0010] Furthermore, the mass ratio of the coarse coal gasification ash slag, the fine coal gasification ash slag, the gangue, the steel slag and the cementitious material is 12 to 20: 6 to 10: 3 to 5: 1 to 3: 3 to 6. The mass of the coarse coal gasification ash slag and the fine coal gasification ash slag is calculated based on dry matter content.

[0011] Furthermore, the mass concentration of the solid components in the low-chromium migration and high-volume coal gasification ash-based cementitious filling material is 50-60%.

[0012] A third technical solution of the present invention is a low-chromium migration and high-volume coal gasification ash-based cementitious filling material, the raw materials of which include coarse coal gasification ash slag, fine coal gasification ash slag, gangue, steel slag, cementitious material, and water in a mass ratio of 12-20:6-10:3-5:1-3:3-6;

[0013] The mass concentration of the solid components in the low-chromium migration and high-volume coal gasification ash-based cementitious filling material is 50-60%;

[0014] The mass of coarse and fine coal gasification ash is calculated based on solids content. The amount of water used must be adjusted based on the moisture content of the coarse and fine coal gasification ash, as well as the mass concentration of the solid components in the desired cementitious filling material. Coarse and fine coal gasification ash contain a significant amount of water, so when determining the amount of water based on the mass concentration of the solid components in the desired cementitious filling material, the water content in the coarse and fine coal gasification ash must be subtracted.

[0015] Furthermore, the raw materials of the cementitious material include mechanically activated coal gasification ash coarse slag, slag and alkali activator in a mass ratio of 1 to 3:1 to 3:1 to 3.

[0016] Furthermore, the particle size of the coal gasification ash coarse slag is 0.15 to 2 mm, excluding 0.15 mm, and is used as one of the aggregates of the filling material.

[0017] Coal gasification ash coarse slag is formed by inorganic mineral molten slag flowing into the bottom of the gasifier and cooling to form particles. It has various shapes, a glassy surface, a low carbon content, and is mainly composed of crystalline minerals.

[0018] Furthermore, the particle size of the coal gasification ash fine slag is ≤0.15 mm, which can fill the gaps in the materials and accelerate the hydration of the cementitious material.

[0019] Coal gasification ash fine slag is carried out by synthesis gas and is separated into fine particles during the subsequent gas purification process. It is mostly powdery, has a high carbon content, and is mainly composed of amorphous glass.

[0020] That is, coarse coal gasification ash slag and fine coal gasification ash slag are two types of solid wastes with different morphologies, sizes and components produced in different parts of the gasifier during the coal gasification process.

[0021] Furthermore, the mechanical activation of the coal gasification ash coarse slag is carried out by drying the coal gasification ash coarse slag (drying to a moisture content of ≤1%) and ball milling the coarse slag to D 50 = 10 to 18 microns and D 90 =38~58 microns are obtained.

[0022] Mechanical activation destroys the dense structure of the glass, exposing the active components of amorphous aluminosilicates in the coarse slag and enhancing its pozzolanic effect.

[0023] Furthermore, the raw materials of the alkaline activator include water glass, NaOH and water in a mass ratio of 8-12:1-3:6-10.

[0024] Furthermore, the modulus of the water glass is 3.3.

[0025] Furthermore, the particle size of the gangue is 2 to 5 mm, excluding 2 mm.

[0026] Furthermore, the preparation steps of the low chromium migration and high content coal gasification ash slag based cementitious filling material specifically include (the flow diagram is as follows Figure 1 shown):

[0027] S1. Using a crusher to crush the gangue, screening out gangue with a particle size of 2 to 5 mm (excluding 2 mm);

[0028] S2. Dry part of the gasification ash coarse residue to a moisture content of ≤1% and then use a ball mill to grind the dried gasification ash coarse residue to D 50 =10~18μm, D 90 = 38 to 58 microns, obtaining mechanically activated coal gasification ash coarse slag (referred to as mechanically activated coarse slag);

[0029] S3, mixing water glass, NaOH and water to obtain an alkaline activator;

[0030] S4, uniformly mixing the mechanically activated coarse slag, slag, alkali activator and a small amount of water to obtain a cementitious material;

[0031] S5. Mix cementitious materials, steel slag, coarse coal gasification ash slag, fine coal gasification ash slag, gangue and water (the amount of water is such that the mass concentration of the slurry, i.e., the solid component, is 50-60%, and the water contained in the coarse coal gasification ash slag and the fine coal gasification ash slag needs to be removed when calculating the amount of water), stir until uniform, and obtain a low-chromium migration and high-volume coal gasification ash-based cementitious filling material.

[0032] The third technical solution of the present invention: an application of the above-mentioned method for solidifying chromium elements in coal gasification ash in solid waste resource utilization or heavy metal solidification.

[0033] The present invention proposes to use an alkali activator to stimulate mechanical activation of coal gasification ash as a cementitious material, and use coal gangue with a particle size of 2 to 5 mm and coarse coal gasification ash slag with a particle size of 0.15 to 2 mm as aggregates to prepare a cementitious filling material, and effectively and stably solidify the chromium element in the coal gasification ash, in order to provide a combined solidification method for the chromium element in a large amount of coal gasification ash-based cementitious filling material for the resource utilization of solid waste and the solidification of heavy metals.

[0034] The present invention discloses the following technical effects:

[0035] The method for solidifying chromium in coal gasification ash provided by the present invention has the following advantages compared with existing methods for treating chromium in coal gasification ash:

[0036] (1) Using steel slag and mineral slag as solidifying materials for the chromium element in coal gasification ash, an alkaline activator is added to stimulate the activity of coal gasification ash, steel slag and mineral slag, thereby achieving the purpose of effectively and stably solidifying the chromium element in the coal gasification ash;

[0037] (2) Mechanical activation is used to destroy the glassy structure in the coal gasification ash, releasing active ions, and then using an alkaline activator to generate a geopolymer gel through a condensation reaction to physically solidify the chromium element; using reducing substances such as low-valent iron in steel slag to reduce highly toxic hexavalent chromium to almost non-toxic trivalent chromium, which is easy to form insoluble hydroxides in an alkaline environment, further reducing its mobility and toxicity; at the same time, the porous structure and large specific surface area of ​​coal gasification ash, steel slag, and gangue can capture hexavalent chromium through physical adsorption or electrostatic action, achieving stable solidification of the chromium element;

[0038] (3) Realize the batch utilization of bulk solid waste, which is economically feasible and environmentally friendly;

[0039] (4) Use alkaline activators to activate the activity of coal gasification ash, steel slag and slag to replace cement, reduce energy consumption and carbon emissions, and lower the cost of filling materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0041] Figure 1 This is a schematic diagram of the preparation process of the low-chromium mobile and high-volume coal gasification ash-based cementitious filling material of the present invention.

[0042] Figure 2 This is the relationship between the uniaxial compressive strength of specimens with different steel slag content, cementitious material content and cementitious filling material content.

[0043] Figure 3 The figure shows the relationship between different steel slag dosages, cementitious material dosages and the concentration of hexavalent chromium in the leachate of cementitious filling material specimens. DETAILED DESCRIPTION

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0046] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0047] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0048] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0049] It should be pointed out that the matters not described in detail in the present invention are conventional operating means in this field and are not the focus of the present invention.

[0050] In the following examples, comparative examples and test examples of the present invention, if room temperature is mentioned, it specifically refers to 20-30°C.

[0051] The “parts” referred to in the following embodiments, comparative examples and test examples of the present invention specifically refer to “parts by mass”.

[0052] Unless otherwise specified, all raw materials used in the following examples, comparative examples, and test examples of the present invention are common commercially available products. Among them, the particle size of the coarse coal gasification ash slag is 0.15 to 2 mm (excluding 0.15 mm), the moisture content is 58%, and the hexavalent chromium content is 105.32 mg / kg; the particle size of the fine coal gasification ash slag is ≤0.15 mm, the moisture content is 63%, and the hexavalent chromium content is 218.34 mg / kg; the cement is P·O 42.5 cement; the gangue is coal gangue; the slag is S95 grade slag; and the FeO content, CaO content, and MFe content of the steel slag are 11.35 wt %, 40.92 wt %, and 12.37 wt %.

[0053] The amount of water added in the following examples and comparative examples is adjusted according to the moisture content of the coarse coal gasification ash slag and the fine coal gasification ash slag and the mass concentration of the slurry to be obtained.

[0054] Example 1

[0055] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0056] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0057] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0058] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0059] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0060] S5. Mix 3 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is calculated so that the mass concentration of the slurry is 60%, and the water contained in the coarse coal gasification ash slag and the fine coal gasification ash slag needs to be shavings when calculating the amount of water), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-volume coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash slag.

[0061] Example 2

[0062] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0063] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0064] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0065] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0066] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0067] S5. Mix 4.5 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the slurry mass concentration is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0068] Example 3

[0069] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0070] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0071] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of less than 1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0072] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0073] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0074] S5. Mix 6 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the mass concentration of the slurry is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0075] Example 4

[0076] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0077] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0078] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0079] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0080] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0081] S5. Mix 3 parts of cementitious material, 2 parts of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the mass concentration of the slurry is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0082] Example 5

[0083] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0084] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0085] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0086] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0087] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0088] S5. Mix 4.5 parts of cementitious material, 2 parts of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the slurry mass concentration is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0089] Example 6

[0090] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0091] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0092] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0093] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0094] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0095] S5. Mix 6 parts of cementitious material, 2 parts of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the slurry mass concentration is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0096] Example 7

[0097] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0098] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0099] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0100] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0101] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0102] S5. Mix 3 parts of cementitious material, 3 parts of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the slurry mass concentration is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0103] Example 8

[0104] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0105] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0106] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0107] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0108] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0109] S5. Mix 4.5 parts of cementitious material, 3 parts of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the mass concentration of the slurry is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0110] Example 9

[0111] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0112] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0113] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0114] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0115] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0116] S5. Mix 6 parts of cementitious material, 3 parts of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the mass concentration of the slurry is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a low-chromium migration and high-dosage coal gasification ash-based cementitious filling material to achieve the solidification of the chromium element in the coal gasification ash.

[0117] Comparative Example 1

[0118] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0119] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0120] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0121] S3. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag and 2 parts of water to obtain a cementitious material.

[0122] S4. Mix 3 parts of cementitious material, 1 part of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the mass concentration of the slurry is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a large-volume coal gasification ash-based cementitious filling material.

[0123] Comparative Example 2

[0124] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0125] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0126] S2. Mix 3 parts of cement (PO 42.5 cement), 1 part of steel slag, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue, and water (the amount of water is such that the slurry mass concentration is 60%), and stir until uniform (stirring time is not less than 4 minutes) to obtain a high-volume coal gasification ash-based cementitious filling material.

[0127] Comparative Example 3

[0128] A method for solidifying chromium in coal gasification ash, comprising the following steps:

[0129] S1. Use a crusher to crush the gangue and screen out gangue particles with a particle size of 2 to 5 mm (excluding 2 mm).

[0130] S2, mechanically activate the coarse coal gasification ash residue, specifically, dry the coarse coal gasification ash residue to a moisture content of ≤1% and then ball mill it to D 50 =10 microns, D 90 =38 microns, obtaining mechanically activated coarse slag.

[0131] S3. Mix 10 parts of 3.3-mol water glass, 2 parts of NaOH and 8 parts of water to obtain an alkaline activator.

[0132] S4. Mix 2 parts of mechanically activated coarse slag, 2 parts of slag, 2 parts of alkali activator and 2 parts of water to obtain a cementitious material.

[0133] S5. Mix 3 parts of cementitious material, 16 parts of coarse coal gasification ash slag, 8 parts of fine coal gasification ash slag, 4 parts of gangue particles and water (the amount of water is such that the slurry mass concentration is 60%), and stir until it is uniform (stirring time is not less than 4 minutes) to obtain a large-volume coal gasification ash-based cementitious filling material.

[0134] Test Example 1

[0135] The chromium mobility and compressive strength of the high-dosage coal gasification ash-based cementitious filling materials prepared in various embodiments and comparative examples were tested. Specifically, the cementitious filling material was poured into a triple mold with a specification of 70.7mm×70.7mm×70.7mm and brushed with silicone oil inside, and placed on a vibrator for 30 seconds. After 24 hours, the mold was removed and placed in a curing box with a temperature of 20°C and a humidity of 95%. After curing for 7 days, a test piece was obtained. The mobility of hexavalent chromium in the test piece was tested by alkaline digestion method. Specifically, the test piece was heated and soaked in a mixed solution of 0.28M Na2CO3 / 0.5M NaOH at 90-95°C for 60 minutes to make the Cr 6+ The uniaxial compressive strength was tested using a WAW-2000D microcomputer-controlled electro-hydraulic servo rock pressure test system with a loading rate of 0.35 mm / min. The test results are shown in Table 1 and Figure 2-3 shown.

[0136] Table 1

[0137] Group Compressive strength (MPa) Hexavalent chromium concentration in leachate (mg / L) Example 1 1.97 2.47 Example 2 2.11 2.36 Example 3 2.15 2.31 Example 4 2.03 2.25 Example 5 2.14 2.17 Example 6 2.19 2.12 Example 7 2.06 2.16 Example 8 2.16 2.09 Example 9 2.21 2.04 Comparative Example 1 1.31 3.56 Comparative Example 2 1.84 3.19 Comparative Example 3 1.69 5.23

[0138] The relationship between different steel slag content, cementitious material content and uniaxial compressive strength of cementitious filling material specimens in Examples 1-9 is as follows: Figure 2 shown.

[0139] The relationship between the different steel slag dosages, cementitious material dosages and the hexavalent chromium concentration in the leachate of the cementitious filling material specimens in Examples 1-9 is as follows: Figure 3 shown.

[0140] Comparing the test data of Comparative Example 1 with that of Example 1, it can be seen that Comparative Example 1, in which no alkali activator is added to the cementitious material, has poor bonding ability due to insufficient activity of the cementitious material, and its strength and detoxication ability are far lower than those of Example 1. Comparing the test data of Comparative Example 2 with that of Example 1, it can be seen that the strength and detoxication ability of Comparative Example 2, in which cement is added (cement is used instead of the cementitious material in Example 1), are slightly lower than those of Example 1. This may be because the gel structure formed by alkali-activated slag is more compact and can effectively solidify chromium ions. Comparing the test data of Comparative Example 3 with that of Example 1, it can be seen that the strength of Comparative Example 3, in which no steel slag is added, is slightly lower than that of Example 1 and its detoxication ability is the worst. This may be because steel slag contains a large amount of low-valent metals, which can form a stable chromite spinel phase, which can effectively solidify chromium ions. Comparing the test data of Examples 1-9, it was found that with the increase of the steel slag content, the compressive strength of the specimen continued to increase, while the concentration of hexavalent chromium in the leachate continued to decrease and gradually approached a certain value; with the increase of the concentration of the cementitious material, the compressive strength of the specimen continued to increase, and the concentration of hexavalent chromium in the leachate after detoxication also continued to decrease; it can be seen that the content of steel slag and cementitious material has a positive effect on the compressive strength and chromium-fixing ability of the material, but the regulating effect of steel slag on the chromium-fixing ability is more obvious, and the regulating ability of the cementitious material on the compressive strength is more obvious. The concentration of hexavalent chromium in the leachate of the mixed sample with a ratio of 2:1 of coarse coal gasification slag (dried and sieved) and fine coal gasification slag (dried and sieved) was determined to be 25.61 mg / L. It can be seen that the hexavalent chromium fixation rate of the cementitious filling material of the present invention is higher than 90%, and meets the leaching toxicity identification standard value.

[0141] The low-chromium migration and high-content coal gasification ash-based cementitious filling material of the present invention has considerable mechanical properties and outstanding chromium-fixing ability, effectively solving the problems of poor stability of solidified chromium elements and large-scale solid waste utilization in traditional coal gasification ash treatment methods, and provides a new method and new material for coal-based solid waste utilization and heavy metal solidification.

[0142] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for solidifying chromium in coal gasification ash, characterized in that: The coal gasification ash is mixed with gangue, steel slag, cementitious material and water to prepare a low-chromium migration and high-volume coal gasification ash-based cementitious filling material to achieve the solidification of chromium elements in the coal gasification ash; The raw materials of the cementitious material include slag and an alkali activator.

2. The curing method according to claim 1, wherein The coal gasification ash includes coarse coal gasification ash and fine coal gasification ash.

3. The curing method according to claim 2, wherein The mass ratio of the coarse coal gasification ash slag, the fine coal gasification ash slag, the gangue, the steel slag and the cementitious material is 12-20:6-10:3-5:1-3:3-6; And / or, the mass concentration of the solid components in the low-chromium migration and high-volume coal gasification ash-based cementitious filling material is 50-60%.

4. A low-chromium migration and high-volume coal gasification ash-based cementitious filling material, characterized in that: The raw materials include coarse coal gasification ash slag, fine coal gasification ash slag, gangue, steel slag and cementitious materials in a mass ratio of 12-20:6-10:3-5:1-3:3-6, and water; The mass concentration of the solid components in the low-chromium migration and high-volume coal gasification ash-based cementitious filling material is 50-60%.

5. The low-chromium migration and high-volume coal gasification ash-based cementitious filling material according to claim 4, characterized in that: The particle size of the coal gasification ash coarse slag is 0.15 to 2 mm, excluding 0.15 mm; And / or, the particle size of the coal gasification ash fine slag is ≤0.15 mm.

6. The low-chromium migration and high-volume coal gasification ash-based cementitious filling material according to claim 5, characterized in that: The raw materials of the cementitious material include mechanically activated coal gasification ash coarse slag, slag and alkali activator in a mass ratio of 1-3:1-3:1-3.

7. The low-chromium migration and high-volume coal gasification ash-based cementitious filling material according to claim 6, characterized in that: The mechanical activation of the coal gasification ash coarse slag is carried out by drying the coal gasification ash coarse slag and then ball grinding it to D 50 = 10 to 18 microns and D 90 =38~58 microns are obtained.

8. The chromium-migrating high-content coal gasification ash-based cementitious filling material according to claim 6, characterized in that: The raw materials of the alkali activator include water glass, NaOH and water in a mass ratio of 8-12:1-3:6-10.

9. The chromium-migrating high-content coal gasification ash-based cementitious filling material according to claim 4, characterized in that: The particle size of the gangue is 2 to 5 mm, excluding 2 mm.

10. Use of the method for solidifying chromium in coal gasification ash according to any one of claims 1 to 3 in solid waste resource utilization or heavy metal solidification.

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